https://phys.org/news/2018-06-physicists-formation-higher-manganese-silicide.html

There is also an ambiguity in their physical properties. To carry out the targeted synthesis of different phases of higher manganese silicides on a silicon substrate, which may be used for thermoelectric and photovoltaic converters, optoelectronic and spintronic devices, is still rather difficult for the scientists. As a rule, to obtain higher manganese silicide thin films, manganese and silicon are placed on the silicon substrate, and afterwards, the system is annealed. In this condition, silicon atoms diffuse from the silicon substrate to the reaction zone and may change the phase formation sequence drastically as the amount of silicon in different higher manganese silicide phases varies within less than 1 percent. Due to such diffusion, it is impossible to obtain a desirable higher manganese silicide phase on silicon substrate just placing the required amount of manganese and silicon, and then heating the system. Silicon atoms from the silicon substrate change the silicon content in the film uncontrollably. The team aimed to resolve this issue during the study.

Two phases of higher manganese silicides were selected for targeted synthesis: Mn4Si7 with the least and Mn17Si30 with the most twisted helices. Like the majority of well-known higher manganese silicides, the first phase has p-type conduction. When the substance is heated, its covalent links are distorted, and free electrons start moving around. This creates holes that move in the direction opposite to that of the electrons. The second phase shows n-type conduction. In this case, the free electrons are the charge carriers.